1. Field of Invention
The present invention relates to a nailing machine in which a drive valve is operated through the cooperation of the trigger operation of a trigger lever and the operation of pressing the contact arm against a work to which a nail is to be driven.
2. Description of Prior Art
The nailing machine is generally constructed so as to be driven through the cooperation of two manual operations, the trigger operation of the trigger lever and the operation of pressing the contact arm against a work to which a nail is to be driven. The nailing machine operates for nail hitting in two modes, a successive nailing mode and a one-shot nailing mode. In the successive nailing mode, nails are successively driven in a manner that an operator presses the contact arm of the machine against a work to which nails are to be driven (referred to as a "nail receiving member"), while pulling the trigger lever. In the one-shot nailing mode, the two manual operations referred to above are required every nail hitting operation. The nailing machine may be categorized into a nailing machine operable only in the one-shot nailing mode, a nailing machine operable only in the successive nailing mode, and a nailing machine operable selectively in the one-shot nailing mode or the successive nailing mode. An example of the nailing machine operable in both the modes is disclosed in Unexamined Japanese Utility Model Publication No. Hei. 1-18294.
In the nailing machine, the on-position of the drive valve is different from the off-position thereof. In a state that the trigger lever is operated, when the contact arm is returned to the bottom dead center, the trigger valve stem is returned to the bottom dead center or to a position before the off position. This return position of the valve stem is selected by operating a select lever of the trigger lever.
The return position select operation is troublesome in a situation where the nailing work requires a frequent switching of the machine mode between the one-shot nailing mode and the successive nailing mode. In handling the nailing machine, an operator sometimes mistakes the operation of the select lever or an impact is accidentally applied to the nailing machine. In this case, the nailing machine operates an unintended mode. This is very dangerous.